Effect of Variability in Ground Motions and Undrained Shear Strength of Soil on Seismic Response of Monopile-Supported Offshore Wind Turbine 

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4. Effect of Variability in Ground Motions and Undrained Shear Strength of Soil on Seismic Response of Monopile-Supported Offshore Wind Turbine 

The increasing demand for renewable energy has spurred the rapid development of offshore wind turbines (OWTs), with monopile foundations being widely adopted due to their cost-effectiveness and simplicity. However, their seismic performance remains a concern,  especially due to ground motion and soil's shear strength variability. This study used ABAQUS to analyse the seismic response of monopile-supported OWT, focusing on the variability in undrained shear strength and ground motions. The analysis considered monopile-supported OWT to be embedded in clay, with soil behaviour modelled using nonlinear p-y springs, while the monopile and the OWT tower were modelled using linear-elastic beam elements. The Rotor Nacelle Assembly (RNA) was represented using a lumped mass with rotary inertia at the top of the OWT tower. Damping of the pile and soil was modelled using a series of dashpots positioned between the pile and soil nodes, parallel to the soil springs. Ground motion variability was assessed by applying synthetically generated earthquake data, while variability in undrained shear strength was introduced using Monte Carlo Simulations (MCS) with coefficients of variation (COV) of 10%, 30%, and 50%.  The findings revealed that variability in undrained shear strength predominantly resulted in increased pile head acceleration with higher COV values, although responses at the mean sea level and tower top remain nearly unchanged between probabilistic and deterministic scenarios. Additionally, the results confirmed that lateral displacement at the tower top satisfies the serviceability design criteria for OWTs. These findings are site-specific and based on modelling assumptions adopted in the present study.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

9 - Monopile design to cyclic loads: quasi-static, dynamic and seismic loads